Stabilization of unsaturated nitriles



United States Patent Louis J. Couvillon, Texas City,

santo Chemical Company, tion of Delaware No Drawing. Application March26, 1954, Serial No. 419,100

Claims. (Cl. 260-4653) Tex., assignor to Mon- St. Louis, Mo, a corpora-This invention relates to the stabilization of unsaturated nitriles.More specifically, this invention relates to the inhibition of thepolymerization of alpha, beta-unsaturated nitriles.

The unsaturated nitriles, particularly the alpha, betaunsaturatednitriles, are extremely useful chemical compounds. Considerablequantities of these materials are used for the preparation of syntheticrubbers and various types of synthetic resins. These materials, however,possess a characteristic which all too frequently hampers not only theirutility, but also the purification techniques commonly employed in theirpreparation. All of these materials exhibit a tendency to polymerizewhen subjected to periods of storage and/or to elevated temperatures.Such polymerization results in a darkening of the unsaturated nitrilemonomer and ultimately in the formation of solid polymer contaminant.

Since most applications or uses of the unsaturated nitriles requirehigh-purity products, these polymerization characteristics present aserious problem in the preparation and storage of finished gradematerial. 'Furthermore, since distillation at elevated temperatures isthe commonly used purification technique, purification is hampered bysolid polymer formation which accumulates in the equipment, ultimatelyplugging the system. To add to this latter problem, impurities presentin crude unsaturated nitriles are frequently of the type whichaccelerate polymerization. For example, acrylonitrile containing smallquantities of acetaldehyde exhibits a greater tendency to polymerizethan does relatively pure acrylonitrile.

Attempts to eliminate this problem have been made in the past by theaddition of inhibitors which retard or prevent the polymerization ofunsaturated nitriles. Unfortunately, the inhibitors heretofore used,while exhibiting some inhibitory effects, have not proven to becompletely satisfactory. To be of practical utility, the inhibitor mustnot impart any undesirable color to the unsaturated nitrile, must besufficiently inhibitory to manifest its effect over extended periods ofstorage, must inhibit polymer formation at elevated temperatures topermit utility in distillation purification techniques, and must bereadily separable from the unsaturated nitrile or inert in subsequentreactions of the inhibited product. The inhibitors heretofore used havenot satisfied all of these requirements.

it is an object of this invention to provide an improved method forpreventing or inhibiting the polymerization of unsaturated nitriles. Itis a further object of this invention to provide an improved method forpreventing the polymerization of unsaturated nitriles by the addition ofan inhibitor which does not possess the deficiencies exhibited by theinhibitors heretofore used. A still further object of this invention isto provide novel stabilized compositions comprising an unsaturatednitrile and an added polymerization inhibitor, which then can besubjected to extended periods of storage or distillation at elevatedtemperatures without exhibiting any significant evidence 2. of polymerformation. Further objects of this invention will become apparent fromthe description which follows.

It has been discovered that the polymerization of unsaturated nitriles,particularly the alpha, beta-unsaturated nitriles, can be greatlyinhibited by mixing therewith a minor amount of 8-hydroxyquinoline. Ithas been found that a composition comprising an unsaturated nitrile anda minor amount of 8-hydroxyquinoline will not exhibit any significantpolymer formation on prolonged periods of storage or when subjected tothe temperatures commonly encountered during purification bydistillation techniques.

The following examples are presented to illustrate the invention but arenot intended to limit it in any manner.

Example I A SOO-ml. round-bottomed flask equipped with a thermometer,stirrer, and sample entry tube is immersed in a constant temperaturebath maintained at 35 C. In this is placed 150ml. of water through whichnitrogen is bubbled at a slow continuous rate. Then 0.1560 g. of NaHSOsis added and the mixture is allowed to attain thermal equilibrium. Afterequilibrium is reached, 10 g. of pure acrylonitrile is added followed by0.405 g. of KzSzOa. The mixture of sodium bisulfite and potassiumpersulfate serves as a polymerization accelerator. Polymerization isallowed to continue for at least one hour following the end of theinduction period indicated by a slight turbidity developing in themixture. After the hour has elapsed, the polymer formed is removed byfiltration, Washed with Water and acetone, and dried at 7783 C.Approximately 7.3 g. of polymer is obtained, indicating a polymer yieldof approximately 73 based on acrylonitrile charged.

Example II The procedure in Example I is repeated with the excep tionthat 0.10 g. of S-hydroxyquinoline is added to the 150 ml. of waterinitially placed in the reaction vessel. In this case, no polymer at allis formed, the solution being perfectly clear.

Example III The test outlined in Example I is again repeated except thatonly 0.01 g. of S-hydroxyquinoline is added to the redox system with the150 ml. of water initially placed in the reaction vessel. Again, nopolymer at all is found after an elapsed time of two hours.

Example IV A sealed test tube containing 20 ml. of crude acrylonitrilecontaining 85-90% acrylonitrile, 37% water, 48% acetaldehyde, and smallquantities of lactonitrile, HCN, cyanobutadiene, and methyl vinyl ketoneis placed in an oven maintained at 80 C. The first cloudiness orturbidity in the solution indicative of polymerization becomes evidentafter about 10 hours.

Example V Example VI Samples of acrylonitrile, methacrylonitrile,crotononitrile, a-ethylacrylonitrile, fl-hexyl acrylonitrile,a,fl-dimethyl acrylonitrile, a-furfuryl acrylonitrile, B-butylacrylonitrile, ,B-(Z-chloroethyl) acrylonitrile, ,B-ethyl acrylonitrile,a-naphthyl acrylonitrile, a-(Z-chlorobutyl) acry- Patented Aug. 7, 1956"lonitrile and. a,-(4-hydroxy phenyl) acrylonitrile are stai ized. bymixing therewith about 1.00. parts. by weight of 8-hydroxyquinoline permillion parts of the nitrile. After extended periods of storage atatmospheric temperatures, no significant discoloration or polymerformation is. evident in these samples.

While the preceding examples have illustrated specific embodiments ofthis invention, obviously substantial variation is possible withoutdeparting from the scope thereof. For example, the quantity of8-hydroxyquinoline used to inhibit the polymerization of the unsaturatednitrile can be varied widely, depending upon the particular nitrile tobe stabilized and the degree of inhibition desired. In general, minoramounts of 8-hydroxyquinoline are used. An advantage, ofS-hydroxyquinoline in such an application as this is the fact that itcan be used in extremely small quantities due to its strong inhibitoryqualities. Concentrations in the range of from about 0.5 to about 1,000parts by weight of 8-hydroxyquinoline per million parts of the nitrileare highly preferred. These low concentrations afford adequate stabilityfor most applications and greatly simplify subsequent processing of thenitrile. Of course, higher concentrations of the inhibitor in thenitrile can be used if desired, resulting in a nitrile monomer even morestrongly inhibited against polymerization.

The inhibitor of the invention can be used to stabilize unsaturatednitriles under many different types of conditions. Thus, it can be usedto inhibit polymer formation in unsaturated nitriles during storageunder atmospheric conditions of light, air, temperature and pressure andduring purification of the crude nitrile monomer. To inhibit polymerformation during distillation of the unsaturated nitrile,8-hydroxyquinoline can be added to the feed stream to the column orintroduced separately at some point in the distillation column.Preferably, the inhibitor is introduced at the top of the column toprovide maximum inhibition throughout the entire system.

The alpha, beta-unsaturatednitriles, represented by the formula R R anwherein the Rs are the same or different and selected from the groupconsisting of. hydrogen and alkyl' radicals containing from one to eightcarbon atoms, respond readily. to the stabilizing effect of theinhibitor disclosed herein. Acrylonitrile, alpha-substitutedacrylonitriles wherein the substituent on the alpha carbon atom isanalkyl radical containing from 1 to 8 carbon atoms, and

beta-substituted acrylonitriles wherein the substituent on the betacarbon atom is an alkyl radical containing from 1 to 8 carbon atoms,represent a class of monomers which polymerize very readily, but can bemost effectively inhi-bited against polymerization by means of8-hydroxyquinoline.

When desired, separation of- S-hydroxyquinoline fromthe-stabilizedunsaturated nitrilemonomer can be accomplished by distillation of thenitrile from the inhibited composition.

What is claimed is:

l. A composition comprising an unsaturated nitrile containing a minoramount of 8-hydroxyquinoline.

2. A composition comprising an alpha, beta-unsaturated nitrilecontaining a minor amount of 8-hydroxyquinoline.

3. A composition comprising a nitrile selected from the group consistingof acrylonitrile, the alpha-substituted acrylonitriles wherein thesubstituent on the alpha carbon atom is an alkyl radical containing fromone to eight carbon atoms, and the beta-substituted acrylonitrileswherein the substituent on the beta carbon atom is an alkyl radicalcontaining from one to eight carbon atoms, containing a minor amount ofS-hydroxyquinoline.

4. A composition comprising a nitrile selected from the groupconsisting. of acrylonitrile, the alpha-substituted acrylonitrileswherein the substituent on the alpha carbon atom is an alkyl radicalcontaining from one to eight carbon atoms, and the beta-substitutedacrylonitriles wherein the substituent on the beta carbon atom is analkyl radical containing from one to eight carbon atoms, containing8-hydroxyquinoline in an amount from about 0.5 to about 1,000 parts byweight per million parts by weight of nitrile.

5. A composition comprising acrylonitrile and from about 0.5 to about1,000 parts by weight of S-hydroxyquinoline per million parts by weightof acrylonitrile.

6. A process for inhibiting the polymerization of an unsaturated nitrilewhich comprises mixing therewith a minor amount of 8-hydroxyquinoline.

7. A process for inhibiting the polymerization of alpha,beta-unsaturated nitriles which comprises mixing therewith a minoramount of 8-hydroxyquinoline.

8. A process for inhibiting the polymerization of a nitrile selectedfrom the group consisting of acrylonitrile, the alpha-substitutedacrylonitriles wherein the substituent on the alpha carbonatom is analkyl radical containing from one to eight carbon atoms, and thebeta-substituted acrylonitriles wherein the substituent on the betacarbon atom is an alkyl radical containing from one to eight carbonatoms, which. comprises mixing therewith a minor amount of8-hydroxyquinoline.

9. A process for inhibiting the polymerization of a nitrile selectedfrom the group consisting of acrylonitrile, the alpha-substitutedacrylonitriles wherein the substituent on the alpha carbon atom is analkyl radical containing from one'to eight carbon atoms, and thebeta-substituted acrylonitriles; wherein the substituent on the betacarbon atom is an alkyl'. radical containing from one to eight carbon,atoms, which comprises mixing therewith 8- hydroxyquinolin-e in anamount from about 0.5 to about 1,000. parts by weight per million partsby weight of nitrile.-

10. A process for inhibiting the polymerization of acrylonitrile whichcomprises mixing therewith from about 0.5, toabout. 1,000 parts byweight of S-hydroxyquinoline per million parts by weight ofacrylonitrile.

References Cited in the file of this patent UNITED STATES PATENTS2,316,197 Tucker Apr. 13, 1943 2,396,555 Cox Mar; 12, 1946 2,609,387Basdekiset al Sept. 2, 1952

1. A COMPOSITION COMPRISING AN UNSATURATED NITRILE CONTAINING A MINORAMOUNT OF 8-HYDROXYQUINOLINE.